linux-kernel - Re: [PATCH] drm/msm/dp: tear down main link at unplug handle immediately

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Date:   Mon, 25 Apr 2022 16:33:18 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dmitry.baryshkov@...aro.org, robdclark@...il.com, sean@...rly.run,
        vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: tear down main link at unplug handle immediately

Quoting Kuogee Hsieh (2022-04-25 15:29:30)
>
> On 4/20/2022 3:38 PM, Stephen Boyd wrote:
> > Quoting Kuogee Hsieh (2022-04-14 14:03:43)
> >
> >> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> >> index 01453db..f5bd8f5 100644
> >> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> >> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> >> @@ -615,24 +598,21 @@ static int dp_hpd_unplug_handle(struct dp_display_private *dp, u32 data)
> >>                  if (dp->link->sink_count == 0) {
> >>                          dp_display_host_phy_exit(dp);
> >>                  }
> >> +               dp_display_notify_disconnect(&dp->pdev->dev);
> >>                  mutex_unlock(&dp->event_mutex);
> >>                  return 0;
> >> -       }
> >> -
> >> -       if (state == ST_DISCONNECT_PENDING) {
> >> +       } else if (state == ST_DISCONNECT_PENDING) {
> >>                  mutex_unlock(&dp->event_mutex);
> >>                  return 0;
> >> -       }
> >> -
> >> -       if (state == ST_CONNECT_PENDING) {
> >> -               /* wait until CONNECTED */
> >> -               dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 1); /* delay = 1 */
> >> +       } else if (state == ST_CONNECT_PENDING) {
> > I take it that ST_CONNECT_PENDING is sort of like "userspace hasn't
> > handled the uevent yet and modeset hasn't been called but the link is
> > setup and now we want to tear it down". The state name may want to be
> > changed to something else.
> yes, how about change to  ST_MAINLINK_READY?

Sure.

> >> @@ -1529,8 +1480,11 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
> >>
> >>          mutex_lock(&dp_display->event_mutex);
> >>
> >> -       /* stop sentinel checking */
> >> -       dp_del_event(dp_display, EV_CONNECT_PENDING_TIMEOUT);
> >> +       state = dp_display->hpd_state;
> >> +       if (state != ST_DISPLAY_OFF && state != ST_CONNECT_PENDING) {
> > Is this to guard against userspace doing an atomic commit when the
> > display isn't connected? Is that even possible?
>
> No, it used to guard follow scenario in timing order,
>
> 1) plugin had been handled and mainlink is ready,
>
> 2)  userspace hasn't handled the uevent yet and modeset hasn't been called
>
> 3) unplugged happen, mainlink be teared down
>
> 4) user space start to response to uevent  and try to enable display.
> (it too late since mainlink had been teared down)
>

Ok. Thanks for clarifying.